This invention relates to a mold for pressing glass plates for liquid crystals or Braun tubes which are useful for electronic calculators, computer and word processor monitors, and molded glass plates for photomasks pressed by using it.
Generally, plastic materials such as polycarbonate, acrylic, epoxy or olefin resin are used for base plates of this type of optical disk, however, the plastic materials have such disadvantages as deterioration by aging under high temperature and high humidity conditions, and limited memory capacity. Accordingly, glass which is hardly affected by environmental conditions has widely been used as material for optical disks.
The glass plates molded by a fusion method or a float method are cut into required shapes after inspection, annealed at a temperature of 300-500.degree. C., and then treated to polish the edges and surface. It is well known that the surface treatment takes considerable time and labor. Also, as glass plates are washed with organic neutralizing agents and pure water after polishing, it was necessary to invest in expensive facilities for waste water treatment.
Recently, as is adopted in the field of small-sized caliber lens manufacturing, a similar molding process has been applied to glass plates which have been treated by the processes of cutting and annealing, and the molded glass plates obtained have satisfactory surface flatness. The pressing mold used in this method is made of a super-hard material on the surface of which graphite or amorphous diamond-type carbon is coated, and the flatness thereof is also highly accurate.
The carbon coating on the surface of the mold is to prevent any scratches on the surface of the molded glass plates, due to air pores remaining on the surface of the mold.
This carbon coat has the superior property of not wetting the glass surface and not adhering to it, but there is a drawback in that it is easy to peel off of the surface of the mold (for example, in the continuous glass molding process, it will peel off when it is used less than 10,000 times).
Therefore, after long-term research and development directed to this problem, the inventor has found and invented that the life of the mold can be greatly extended by performing ion sputtering on the surface of the super-hard material prior to the carbon coating. It is also found that mechanical characteristics such as anti-friction, anti-wear, and anti-fatigue properties have been significantly improved.